Transmission system

ABSTRACT

The invention contemplates systems for transmitting signals or the like via selected ones of a number of separate paths by establishing a null across a selected path location to enable the path effective to transmit a signal. One disclosed embodiment of the invention is a binary memory storage unit. Another disclosed embodiment is an electrical intercommunication system. Still another disclosed embodiment features an adjustable iris.

United States Patent Sandoval Sept. 24, 1974 TRANSMISSION SYSTEM Primary Examiner-Harold I. Pitts [76] Inventor: Dante J. Sandoval, 6412 Pear Ave., f f 'z Agem or F mwatts Hoffmann Fisher &

Cleveland, Ohio 44102 [22] Filed: Sept. 4, 1973 [57] ABSTRACT [21] Appl' 393,965 The invention contemplates systems for transmitting signals or the like via selected ones of a number of 52 us. c1. 340/147 R, 340/147 LP separate paths y establishing a across a selected [51] Int. Cl. H04q 3/00 P location to enable the P effective to transmit a [58] Field of Search 340/147 R, 147 LP signel- One disclosed embodiment f he inven ion is a binary memory storage unit. Another disclosed em- [56] References Ci bodiment is an electrical intercommunication system.

another disclosed embodiment features an adjust- 3,610,960 10 1971 Hofstein 307 251 able 3 7l7 4, l95 11/]973 Schulthess 340/324 R 20 Claims, 6 Drawing Figures mmmwwm amass 4. SHEET 10F 2 TRANSMISSION SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new and improved system for transmitting information or electromagnetic energy via selected paths of a number of parallel paths.

2. Prior Art The prior art has proposed various systems and arrangements for transmitting information or power via selected ones of parallel paths but in the main these prior art proposals have been of relatively complicated construction and have exhibited functional disadvantages. Some prior art systems have been formed by electrical networks in which a succession of parallel voltage responsive circuits were connected across a power supply via some form of resistive conductor. The voltage across all of the circuits was increased until an initial circuit was rendered conductive in response to the applied voltage. Conduction of the initial circuit re sulted in energization of a load or in transmission of a signal via that circuit. Continued increase of the voltage applied across the parallel circuits resulted in a second parallel circuit being rendered conductive in response to the voltage applied across it. When this occurred, the voltage across the first circuit was increased so that the first circuit tended to remain in a conducting state.

In order to achieve selectivity, the prior art proposed feedback interconnections between the successive parallel circuits so that, for example, when the second circuit in a succession was rendered conductive, the initial circuit was consequently rendered nonconducting even though the applied voltage level was otherwise sufficient to maintain the first circuit conducting. The feedback interconnections have complicatedthe prior art constructions.

Examples of this kind of electrical circuit are disclosed by US. Pat. No. 3,610,960 and U.S. Pat. No. 3,358,157.

The prior art proposals utilized power supply current to operate the load and/or provide a signal transmitted by the selected conducting circuit. This type of operation resulted in fluctuations of the voltage levels applied across the various parallel circuits particularly during transition periods in which two parallel circuits were momentarily conductive. In order to avoid such voltage fluctuations the resistive conductors had to be constructed to assure substantial voltage drops between successive parallel circuits, or the power supply had to be provided with a sensitive regulator.

The principle of operation of the prior art proposals has been such that use of prior art circuitry of the character referred to has been restricted to a relatively few applications, such as an analog to digital converters.

SUMMARY OF THE INVENTION The present invention contemplates systems for selectively transmitting information, power or electromagnetic energy via a series of independent parallel paths. The principle of operation of the invention enables a wide variety of usages, and systems embodying the invention can be extremely simple, compact, capable of operation at high speed and utilize small amounts of power.

An important feature of the invention resides in applying voltages across parallel conductors so that when the differential voltage between locations on the conductors is substantially zero, information or power signals or electromagnetic energy can be transmitted between the locations.

The zero differential potential location can be scanned or moved stepwise along the conductors so that transmission of the signals, etc. can occur via selected paths between the conductors. The scanning or stepping of the zero potential locations can be accomplished with great speed and when applied across selected locations, the transmission of signals, etc. does not draw appreciable current from the voltage establishing power supply.

In a preferred construction of the invention, a network defining a plurality of independent paths is connected in parallel across a selection system. The selection system comprises a power supply, parallel conductors connected across the power supply and between which the paths extend, and at least a selector element for varying the voltage level applied across at least one conductor. The paths are selectively rendered effective to transmit signals or information by controlling operation of the selection system.

At least one parallel conductor is resistive along its length so that the applied power supply voltage drops proceeding along that conductor. The parallel paths are connected to the resistive conductor at spaced apart locations so that the voltage applied across each path between the conductors is unique. The selector element is operable to enable the voltage applied across the resistive conductor to shift relative to a reference level and when the selector element is operated, a null, or zero potential differential, is establishable across selected paths.

The parallel paths are constructed so that they compare the voltage levels at their junctures with the conductors and are rendered effective to transmit information or power only when a null, or a substantially zero voltage differential, is established across them. The location of the null is shifted by the selector element so that the null location can be scanned along the parallel paths or can be adjusted to place the null across a given selected path. When a given path is rendered effective, information, power or electromagnetic energy can be transmitted via that comparator path but not via other paths having voltages applied across them.

The transmitted information or power is supplied from a source which is separate from the selection system power supply.

One disclosed embodiment of the invention is a memory unit which includes a selection system associated with parallel memory storage comparator paths. Each of the parallel comparator paths is constructed so that it can be conditioned to transmit a signal or not to transmit a signal when a null is established across that path. Hence each comparator path can store binary information.

The selection system can either scan the null across the comparator paths at a prearranged rate or can be operated to establish the null across a selected path to permit selective access to the stored information. In any event the location of the null is determinable so that the binary information stored by each path is-accurately and quickly retrievable.

In another disclosed form of the invention, information can be transmitted between selected remote locations and a master station by providing signal transmitting and receiving devices associated with each of the parallel comparator paths and with the master station. The selection system functions to select one of several comparator paths by shifting the null along the parallel conductors to the desired path.

Another embodiment of the invention provides an electrically controlled iris which is devoid of the usual iris defining mechanical parts which must be adjusted to control the aperture size. In this embodiment of the invention an assembly is provided in which the selection system controls the passage of electro-magnetic energy through parallel comparator paths defined, in effect, by a body of liquid crystal material. The parallel conductors of the selection system are defined by first and second parallel extending electrically resistive sheets of transparent material.

The liquid crystal material is disposed between the conductor sheets. The liquid crystal material in the desired electromagnetic frequency ranges (e.g. the visible light portion of the spectrum), is transparent where the potential across the crystal material between the sheets is nulled, or approximately zero, and is opaque where the applied potential is not approximately zero.

The power supply of the selection system applies a DC. potential across the ends of the first resistive sheet so that the applied voltage drops proceeding across the sheet. A DC. potential is likewise applied across the corresponding ends of the second sheet with the polarity of the applied voltage reversed. This creates a band, parallel to the sheet ends and across the liquid crystal material, along which a null exists across the crystal material. The liquid crystal material is transparent along this band allowing the passage of electromagnetic radiation. The selection system, by controlling the voltage magnitudes of the voltages applied across the conductor sheets, can change the width and location of the zero potential transparent band.

A duplicate second assembly is juxtaposed with the first assembly and is oriented so that the transparent band formed by the second assembly extends transverse to the direction of extent of the first band and thus a generally rectangular aperture, formed by the area of intersection of the bands, is provided by the assemblies.

The size of the aperture is controllable by varying the power supply voltage applied across the conductive sheets of the assemblies. When the power supply voltage is minimized, virtually the entire area of the assemblies is transparent to the electromagnetic radiation. As the applied power supply voltage is increased the widths of the transparent bands become progressively narrower and the aperture size is reduced.

An iris constructed according to the principles of the invention also enables the location of the aperture to be shifted to any desired location in the assemblies.

Other features, advantages and uses of the present invention will become apparent from a consideration of the following detailed description made with reference to the accompanying drawings which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 2 is a schematic diagram of a system for transmitting information between a master location and a selected one of a number of remote locations according to another preferred embodiment of the invention;

FIG. 3 is a schematic perspective view of an adjustable iris embodying the present invention:

FIGS. 4, 5 and 6 show further constructional features of the iris of FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS A binary memory unit 10 embodying the present invention is illustrated in FIG. 1 of the drawings. The binary memory unit 10 comprises a network 12 of memory storage comparator paths individually indicated at 12a-12c. The paths 12a-12c are individually selectively rendered effective to provide stored binary memory information by operation of a selection system 14. Binary information from individual comparator paths, in the form of the presence or the absence of a singal, is obtained by signal circuitry generally indicated at 16. The selection system functions to selectively establish a null across one of the comparator paths while providing a DC. voltage across the remaining paths. The signal circuitry provides an A.C. input signal which can be transmitted to a signal output only by a path which is conditioned to transmit and which has a DC. null established across it. Memory information is produced whenever a null is established across a desired comparator path since the path will transmit the signal if so conditioned and will not transmit the signal if not so conditioned.

THE COMPARATOR PATHS While only three comparator paths 12a-12c are illustrated it should be appreciated that an extremely large number of these paths can be provided in the system 10 so that the binary information stored by the system can be quite large. The paths 12a-12c are each conditionable to transmit signals and when so conditioned each path compares the voltage levels existing at its opposite ends. When the voltage level at the opposite ends of such a comparator path are equal (i.e. when a null or zero potential exists across the path) the path is effective to transmit a signal indicating the character of the binary information stored by the path. If the path is not conditioned to conduct, even though a null is established across it the path will not transmit. This provides binary information by reason of the absence of the signal transmission.

The paths 12a-12c are identical and accordingly only the path 12a is described in detail. The path 12a comprises a conductor 20a having opposite end junctions 22a, 24a by which the conductor 20a is connected across the selection system 14. Oppositely poled diodes 26a, 28a are connected in the conductor 20a between the junctions 22a, 24a with the cathode electrodes of each of the diodes 26a, 28a connected to a junction 30a which is grounded through a path conditioning circuit comprising a switch 32a and an impedance ele ment formed by a resistor 34a.

When the switch 32a of the conditioning circuit is open, the path is conditioned so that it cannot transmit A.C. signals even though the DC. voltage across the junctions 22a, 24a is nulled. When the switch 32a is closed, the path 12a is conditioned to transmit signals, but only when the DC. voltage across the junctions 22a, 24a is nulled. The resistor 34a is large so that conduction to ground via the closed switch 32a is minimized. It should be appreciated that the path conditioning circuitry could be provided by a suitable solid state circuit which would provide relatively high impedance when the path is conditioned to conduct and infinite impedance when the path is conditioned not to conduct. Use of such a solid state device would enable the network 12 and associated portions of the selection system 14 to be formed by an integrated circuit thus enabling a great number of memory storing paths to be formed in a relatively small volume package.

The comparator path 12a is constructed so that when a differential DC. voltage is applied across the junctions 22a, 24a. the comparator path is nonconductive regardless of the position of the switch in the path conditioning circuit. When the voltage level with respect to ground at the junction 22a is greater than the voltage level with respect to ground at the junction 24a, the diode 26a is forward biased while the diode 28a is back biased and the path 12a is nonconductive to both AC. and DC. When the voltage level with respect to ground at the junction 24a is greater than the voltage level with respect to ground at the junction 22a, the diode 28a is forward biased while the diode 26a is back biased and the path 12a is again nonconductive.

Assuming that the switch 32a is closed to condition the path 12a for conduction, when the voltage at the junction 24a with respect to ground is equal to the voltage level with respect to ground at the junction 22a, the diodes 28a, 26a are both forward biased and conducting through circuits established from the junctions 22a, 24a, through the respective diodes and to ground via the switch 32a and the resistor 34a. When the diodes 26a, 28a are both forwardly biased, the path 12a abruptly becomes conductive to applied AC. power and the path 12a is thus capable of transmitting A.C. signals.

The path 12b is illustrated as conditioned against conduction since the switch 32b is open. When a null is established across the end junctions 22b, 24b no A.C. signal can pass since the diodes 26b, 28b are not forwardly biased.

The impedances of the resistors 34a-34c determine the amplitude, or strength, of the AC. signal transmitted by the respective paths l2al2c. If desired, the resistors 34a-34c can be potentiometers which provide preselectable impedance levels sothat the signals transmitted by the respective paths can have different, predetermined strengths. As the individual impedance values are reduced, the signal strength is increased and vice-versa.

A suitable actuator 40 for the switches 32 is schematically illustrated in FIG. 1. The switch actuator 40 is constructed so that individual ones of the switches 32a-32c can be opened or closed as desired to effectively store binary information. It should be understood that the actuator 40 can be formed by suitable circuitry in the event that the switch 32 and resistor 34 are replaced by solid state devices as noted above.

THE SELECTION SYSTEM The selection system 14 functions to selectively apply a null across the individual paths l2a-l2c to enable retrieval of binary information from the comparator paths. In the preferred embodiment of the invention the selection system 12 comprises a DC. power supply indicated by the character B+, parallel resistive conductors 52, 54 connected across the power supply to ground, and a selector mechanism 56 for enabling the retrieval of the binary information from selected comparator paths of the network 12.

The conductor 52 is preferably formed by suitable material which provides for a gradual, substantial power supply voltage drop along its length. The paths l2a-l2c are connected to the conductor 52 via the junctions 22a-22c, respectively. The junctions are connected to the conductor 52 at electrically spaced locations along the conductor so that the voltage level with respect to ground at each junction 22a-22c, respectively, is unique (i.e. it is different from the voltage level at the remaining junctions). The construction of the conductor 52 as described provides resistances indicated by the characters rl-r4 between successive comparator path junctions.

The conductor 54 as illustrated is formed by a voltage divider including series connected resistors 60, 62 between which an output voltage junction 64 is located. The conductor 54 could be constructed the same as the conductor 52, if desired, with the junction 64 formed in the conductor at a location to provide an output voltage proportional to the power supply voltage. The junctions 24a-24c of the paths l2a-l2c respectively are electrically connected in common to the output voltage junction 64 so that the voltage level with respect to ground at the junctions 24a-24c are all the same. The power supply voltages across each comparator path are thus each of different magnitude or polarity and only one comparator path can have a null established across it. I

The selector mechanism 56 is effective to change the voltage level with respect to ground applied across the conductor 52 from the power supply B+ to thereby change the respective voltages at the junctions 22a-22c with respect to the voltage at the output junction 64. This permits a null to be established across any individual selected comparator path of the network 12. ln the preferred embodiment, the selector mechanism 56 comprises selector potentiometers 70, 72 at opposite ends of the conductor 52. The wiper of each of the potentiometers 70, 72 is connected by a linkage 74 to an actuator 76. When the actuator 76 is operated the effective resistances of the potentiometers 70, 72 are changed simultaneously.

The potentiometers 70, 72 are operated to shift the level of the voltage applied across the conductor 52 while maintaining the power supply current substantially constant. This is accomplished by connecting the potentiometers 70, 72 to the linkage 74 so that 'when the actuator 76 is operated in one direction the resistance of the potentiometer increases while the resistance of the potentiometer 72 decreases correspondingly and vice-versa when the actuator operates in the opposite direction. By way of example, when the resistance of the potentiometer 72 is minimum the resistance of the potentiometer 70 is maximum so that the voltage drop across the potentiometer 72 is very small and the voltage level with respect to ground at the end of the conductor 52 adjacent the potentiometer 72 is substantially at the power supply voltage level. Conversely, when the actuator 76 operates the potentiometers to maximize the voltage drop across the potentiometer 72 while minimizing the drop across the potentiometer 70, the voltage level with respect to ground at the end of the conductor 52 adjacent the potentiometer is minimum. In this manner, although the magnitude of the voltage drop across the conductor 52 is constant, the level of the voltage applied across the conductor 52, with respect to ground, is varied according to the I operation of the actuator 76. The construction of the potentiometers 70, 72 enables the total resistance of the potentiometers and the conductor 52 to remain constant throughout the range of operation of the actuator.

The actuator 76 may be an electric motor operated at a known speed to scan the voltage applied across a conductor 52 so that successive paths of the network 12 are enabled to provide memory information. Alternatively, the actuator can be operated to change the voltage across the conductor 52 stepwise between predetermined levels to access a desired path of the network 12.

Although the selector mechanism 56 is illustrated as comprised of potentiometers, a linkage and a linkage actuator, the selector mechanism can be constructed by suitable solid-state circuitry capable of performing the same functions. The construction of such equivalent solid-state circuitry will enable the selector mechanism 56 to be formed by the use of integrated circuit techniques to thus minimize the size of the system 10.

THE SIGNAL CIRCUITRY The signal circuitry 16 functions to provide an input signal which is applied across the conductors 52, 54 so that when an individual comparator path of the network l2 has been conditioned to conduct and a null has been established across that path, the path transmits the input signal to an output device. The circuitry 16 comprises an input transformer 80 having a primary winding 82 connected to an A.C. power supply and a secondary winding 84 which is connected in the selection system 14 at a desired location. In the illustrated embodiment, the secondary winding 84 is connected to the conductor 54 however if the conductor 54 is formed by an integrated circuit element, the winding 84 can be connected externally of the integrated circuit.

The signal circuitry output device comprises an output transformer 86 having a primary winding 88 connected between the network 12 and the outputjunction 64, and a secondary or output, winding 90 which is in turn connected to suitable signal utilization circuitry generally designated at 92.

When any path of the network 12 is conducting, a circuit is established through the input transformer secondary 84, the output transformer primary 88, and the conducting comparator path. This results in an output signal across the winding 90 to the utilization circuitry 92. When the selector circuitry has been operated so that none of the paths of the network 12 have a null established across them, or when a null is established across a given comparator path which is conditioned not to conduct, a circuit through the windings 84, 88 cannot be completed and hence no singal is provided to the utilization circuitry 92.

In the preferred and illustrated embodiment, the actuator 76 and the utilization circuitry 92 are interrelated so that the condition of the selector mechanism 56 effects operation of the utilization circuitry 92. By this interconnection, the absence of the signal to the utilization circuitry 92 across a comparator path which is conditioned against conduction has the effect of providing the binary not" to the utilization circuitry.

FIG. 2 illustrates another embodiment of the invention by which circuitry schematically indicated at functions to enable transmission of signals between a master station and a selected one of a number of remote locations. As an example. the circuitry 100 could be used in an intercommunication system by which signals can be transmitted between a master station (for example, one room in an office) and a selected one of a series of remote stations (in other rooms of the office). The system 100 comprises a network 112 of parallel comparator paths of which only three are illustrated at 112a-112e, a selection system generally indicated at 114 by which a remote station is selected for communication with the master or central station, and signal circuitry generally indicated at 116 associated with the network 112 and the selection system 114 for the transmission and reception of signals.

The network 1 12 is electrically similar to the network 12 described in reference to FIG. 1 and each of the paths 112a-1120 are identical. Accordingly only the path 112a is illustrated and described in detail. The path 112a comprises a conductor 120a having opposite end junctions 122a, 124a for connection the paths 112a across the selection system 114. The path 112a comprises diodes 126a, 128a which have their cathode electrodes connected to ground through a common impedance element 134a. The path 112a functions so that when a null is established across the junctions 122a, 124a, the diodes 126a, 128a are both forwardly biased thus permitting the path 1120 to conduct A.C. Whenever the voltage levels with respect to ground at the junctions 122a, 1240 are different, one or the other of the diodes 126a, 128a is back biased and the path 112a is rendered nonconductive to A.C.

The selection system 114 is substantially the same as that described above in reference to FIG. 1 and accordingly like parts are indicated by corresponding primed reference characters and are not further described except in their functional interrelationship with the remaining components of the circuitry 100.

The signal circuitry 116 comprises a signal transmitting and receiving transformer which is disposed at the master station, and remote signal transmitting and receiving transformers l42a-l42c which are associated with the comparator paths 112a-112e, respectively, of the network 112. The transformer 140 comprises a winding 144 which is connected to a signal generating and receiving unit 146 which, in the case of an intercommunication system, can be a combination speaker and microphone circuit. The winding 144 is inductively coupled to a winding 148 which is connected in a circuit between the network 112 and the output junction 64' of the conductor 54.

The remote signal transmitting and receiving transformer l42a-142c are all identical and accordingly only the transformer 142a is described in detail. The transformer 142a comprises a winding 1500 connected to a unit 152a like the unit 146. The winding a is inductively coupled to a winding 154 which is connected in series between the cathodes of the diodes 126a, 1280. The winding 154 is provided with a center tap which is grounded through the resistor 134a so that the small D.C. currents which flow through the diodes 126a, 128a to ground via the resistor 134a are balanced when a null is established across the path 112a.

In order to communicate between the master station and a remote station the actuator 76 is operated to establish a null across, for example, the comparator path 112a. When this has been accomplished the diodes 126a, 128a are both forwardly biased by a small current which flows through each diode to ground via the resistor 134a and the comparator path 112a is conductive to A.C. Signals generated by the unit 146 are transmitted via the transformers 140, 142a to the unit 1520 and vice versa so that communications can be had between the master station and the remote station.

Since a differential voltage is applied across the remaining comparator paths 112b, 112e, the signals which are transmitted between the master station to the transformer 142a, at the remote station cannot be received by the transformers 142b, 142C of the remaining remote stations.

Operation of the actuator 76' can be controlled in any suitable manner from the master station and/or from any of the remote stations. It should be appreciated that if the circuitry 100 is employed in connection with an intercommunication system the actuator 76' is operated in a step-wise fashion to establish a null across a given selected comparator path corresponding to the desired remote location.

A circuit of the character disclosed in FIG. 2 can also be utilized to sense conditions at remote locations and when so utilized the actuator 76' is operated in continuous fashion so that the null is, in effect, scanned across the comparator circuits of the network to quickly monitor the conditions in succession.

FIGS. 3-6 illustrate a collimator or iris unit 200 which, for the purpose of this description, functions to permit visible light to pass through a transparent window. The iris unit 200 is formed by identical assemblies 202, 204 which cooperate to form the aperture through which the light (or electromagnetic radiation of other frequencies) may pass the the size of which aperture is adjustable without requiring mechanically movable aperture forming parts. Since the assemblies 202,204 are identical only the assembly 202 is described in detail.

The assembly 202 comprises a body of liquid crystal material 206 which defines, in effect, a comparator path network through which light is selectively transmitted, and a selection system 208 for selectively determining the location and size of the light transmitting path areas through the material 206. Liquid crystal material 206 has the property of being opaque to visible light when a voltage is established across the material but which is transparent in the absence of a voltage differential applied across it. The liquid crystal material is confined to a volume which has generally rectangular major surfaces and has a relatively small thickness. When equal voltages exist at corresponding locations on the major surfaces of the body 206 the material between these locations is transparent to visible light while the material between other corresponding locations on the major surfaces are opaque if a voltage differential-exists between such corresponding locations.

The liquid crystal material can be of any suitable type such as the materials referred to in an aritcle by Joseph A. Castellano at page 64 of Electronics magazine published July 6, l970.

The selection system 208 controls the position and size of corresponding locations on the major surfaces of the crystal network material 206 to thus govern the transmission of light to the assembly 202. The selection system 208 comprises electrically resistive transparent conductor sheets 210, 212 which are electrically connected in parallel across a suitable variable voltage DC. power supply, indicated schematically at 214, and

a selector arrangement for determining the locations along the sheets across which a null is located.

The sheets 210, 212 are generally rectangular members having a relatively small thickness which are supported in parallel extending relationship to each other by a dielectric support frame 216 which sealingly extends about their peripheries to maintain them in position and to seal the volume defined between the sheets. The crystal network material 206 is sandwiched between the sheets 210, 212 and maintained in place by the supporting and sealing frame 216.

The opposite end faces of the sheets are covered by end coatings 220 of highly conductive material which are in turn connected to the power supply 214. The coatings 220 permit the currents flowing through the sheets to be distributed uniformly across their ends. The sheets 210, 212 can be formed from any suitable transparent sheet material which is resistively conductive itself or which has a transparent resistively conducting coating applied to the major surface in contact with the liquid crystal material 206. The opposed ends 210a, 21% of the sheet 210 are connected between the positive and negative terminals of the power supply 214, respectively, while the opposed ends 212a, 212b of the sheet 212, which correspond to the sheet ends 210a, 21%. are connected between the negative and positive terminals of the power supply, respectively. Thus currents flowing through the sheets 210, 212 are oppositely directed. The connections to the power supply are made by suitable conductors which extend through the frame 216 and are joined to the respective end coatings 220.

Due to the above described connections to the power supply, the voltage level at the sheet end 210a is always positive withrespect to the voltage level at the sheet end 2101: and the voltage at the sheet end 2121) is always positive with respect to the voltage at the sheet end 212a. When the voltages applied across the sheets are the same, a null is established across the confronting major faces of the sheets 210, 212 substantially medially between their ends and along a band indicated at 230 which extends parallel to the ends of the sheets. Since substantially no voltage differential is established across the liquid crystal network body 206 along the null band, the liquid crystal material is rendered transparent along the band. Hence the entire assembly 202 is transparent along the band'which is indicated in FIG. 3 at 230.

The selection system 208 is effective to shift the voltage levels applied across the sheets 210, 212 to shift the location of the band 230 to desired locations between the ends of the sheets. The selection system includes potentiometers 232, 234 connected at opposite ends of the sheet 210 which are ganged together by a suitable linkage 236 to operate in the same manner described above in reference to the potentiometers 70, 72 of the memory unit in FIG. 1.

Potentiometers 238, 240 are connected at opposite ends of the sheet 212 to control the voltage level with respect to ground applied across the plate 212. The potentiometers 238, 240 are ganged for simultaneous operation by a linkage 242 which is schematically shown. In the illustrated embodiment of the invention, the potentiometer linkages 236, 242 are operated together via a suitable control knob 244 (see FIG. 4) so that the band 230 is shifted along the assembly as desired.

The assembly 202 could be constructed by replacing the potentiometers 238, 240 with fixed resistors and by providing a low resistance sheet 212 between them. The voltage with respect to ground along the sheet 212 would thus be fixed and substantially constant. Shifting of the voltage along the plate 210 in such a construction enables the band 230 to shift along the assembly.

As noted previously, the power supply 214 is a variable voltage power supply and may be constructed in any suitable manner. The power supply voltage is variable to change the width of the transparent band through the assembly 202. When the voltage output from the power supply is relatively low, or is cut off entirely, the entire assembly 202 is transparent because no voltage differential is applied across the body of crystal network material 206. As the power supply voltage is increased, the differential voltage across the crystal material everywhere but at and adjacent the precise null location is increased so that the transparent band 230 becomes increasingly narrower as the power supply voltage is increased. Hence, by changing the applied voltage from the power supply the width of the transparent area of the assembly 202 is effectively governed without requiring complicated mechanically adjustable iris forming parts. The power supply voltage can be controlled by a suitable knob 246 linked to the power supply.

The assembly 204 is identical to the assembly 202 and therefore is only partially shown. Parts of the assembly 204 which are the same as parts described above are therefore indicated by corresponding primed reference characters. The assembly 204 differs from the assembly 202 only in that the sheets 210', 212 of the assembly 204 are oriented at 90 with respect to the sheets 210, 212 of the assembly 202. Thus the transparent band 230' extending through the assembly 204 extends at right angles with respect to the transparent band 230 of the assembly 202. The assemblies 202, 204 are juxtaposed, as illustrated in FIG. 6, the area of intersection of the bands 230, 230' forms a square or rectangular aperture in the form of a transparent window 260 which permits light to pass through the unit 200. A thin transparent insulator 250 is disposed between the assemblies to isolate the sheets 212 and 210 of the adjacent assemblies. The frame 216 extends about both assemblies to maintain them in position with respect to each other.

By controlling the variable power supplies of the assemblies 202, 204 in the manner described above the area and shape of the aperture is readily varied. The linkages 236, 242 and 236', 242' of the assemblies 202, 204 are independently operated so that the bands 230, 230' can be shifted in directions transverse to their extents. This enables the apertures to be shifted to any desired location on the iris unit.

FIG. 4 illustrates the iris unit 200 with the assemblies juxtaposed. The window 260 of the iris unit 200 is defined by the area of intersection of the transparent bands 230, 230' of the assemblies. The four corner areas of the iris unit are those in which opaque portions of both the assemblies 202, 204 overlie each other.

FIG. 5 illustrates the iris unit 200 in a condition in which the power supply voltages of each of the assemblies is reduced relative to the power supply voltage which is applied in FIG. 4 and the area of the window 260 is increased accordingly.

While three embodiments of the present invention have been illustrated and described herein in considerable detail the present invention is not to be considered limited to the precise constructions shown. Other adaptations, modifications and uses of the invention may occur to those skilled in the art and it is the intention to cover all such adaptations, modifications and uses which come within the scope or spirit of the appended claims.

What is claimed is:

1. In a system for transmitting perceptible signals:

a. first resistive conductor means;

b. second conductor means;

c. electric power supply means connected to said first and second conductor means;

d. signal transmitting means defined by a plurality of separate parallel paths electrically connected between said first and second conductor means, said paths connected to said first conductor means at electrically spaced locations and each comprised of electrically responsive means rendered effective to transmit information in response to the application of substantially zero voltage differential across such path; and.

e. selector means cooperatively related with said power supply means and at least one of said conductor means for selectively applying substantially zero voltage differentials across selected ones of said paths.

2. A system as claimed in claim 1 further including signal means defining a source of information for tranmission by individual ones of said path when such paths are rendered conductive.

3. A system as claimed in claim 2 further including a plurality of control means each associated with a respective parallel path, each of said control means governing the ability of its respective path to transmit a signal from said signal means when said path is rendered effective.

4. The system claimed in claim 2 wherein said signal means comprises second electrical power supply means connected in a circuit across said paths, said circuit for said second power supply means being completable only through those paths which are rendered effective to transmit signals, and output means for detecting completion of a circuit across said second power supply means.

5. The system claimed in claim 4 further comprising conditioning means associated with respective ones of said paths for controlling the conduction of a respective path which is rendered effective to transmit signals, said conditioning means having a first condition wherein a circuit through said respective path is interrupted when said path is rendered effective and a second condition wherein said respective path is conductive when rendered effective.

6. The system claimed in claim 4 wherein said second power supply means comprises an alternating current source and said output means comprises at least an element for detecting alternating current power in a circuit connected across said second power supply means.

7. A system as claimed in claim 1 wherein said power supply means comprises a DC. power supply, and said selector means comprises an impedance element connected in circuit with said DC. power supply means and said first conductor means, and mechanism for varying the impedance of said element.

8. The system claimed in claim 1 wherein said first 4 and second conductors comprise transparent sheets and said signal transmitting means comprises a body of liquid crystal material, said sheets disposed on opposite sides of said body of liquid crystal material to define a radiation transmitting assembly wherein signals in the form of radiation are passed through the assembly along paths extending through said conductors and said liquid crystal material, said power supply means providing a substantially steady state voltage across each of said sheets.

9. The system claimed in claim 8 wherein the voltage across said sheets provides a transparent band extending across said sheets and through said liquid crystal material to enable electromagnetic radiation to pass through said sheets and crystal material along said band.

10. The system claimed in claim 9 wherein said selector means is effective to shift the location of said band relative to said sheets and crystal material.

11. The system claimed in claim 10 wherein said power supply means includes structure for providing a variable voltage output for adjustably controllingithe width of the band.

12. The system claimed in claim 8 further comprising a second radiation transmitting assembly juxtaposed with said first assembly, said second assembly comprising first and second transparent sheet-like conductors having a body of liquid crystal material interposed between them, power supply means for producing a substantially steady state voltage across each of said conductors of said second assembly, said first and second assemblies oriented with respect to each other so that the radiation transparent bands extend in directions transverse to each other to produce a radiation transparent aperture through said first and second assemblies.

13. The system claimed in claim 12 further comprising second selector means associated with said second assembly, said first and second selector means operable to shift the positions of the respective radiation transmitting bands relative to said assemblies to adjustably change the location of said aperture relative to said assemblies.

14. In a system for selectively transmitting information:

a. means defining an electric power supply;

b. first resistive conductor means connected across said power supply means;

c. second conductor means connected across said power supply means;

d. means defining a plurality of parallel information transmitting paths electrically connected between said first and second conductor means, said paths connected to said first conductor means at electrically spaced locations;

e. each of said paths individually rendered effective to transmit information only when the power supply voltage applied across such path between said first and second conductors is substantially zero; and, f. selector means cooperatively related with said 5 power supply means and at least one of said first and second conductor means for changing the power supply voltages applied across said paths so that said paths are selectively and individually rendered effective to transmit information.

15. The system claimed in claim 14 further comprising means for transmitting information between said conductors via only said paths which are rendered effective.

16. The system claimed in claim 15 wherein said 5 means for transmitting information provides for the passage of electromagnetic energy through said paths which are rendered effective.

17. The system claimed in claim 14 wherein said power supply means comprises a DC. power supply and said paths each comprise at least a circuit element having a variable impedance to the passage of electromagnetic energy via said path, said circuit element having a first impedance when substantially zero power supply potential is applied across said path and a substantially different impedance when a power supply voltage differential is applied across said path.

18. The system claimed in claim 17 wherein said at least one circuit element comprises first and second oppositely poled diodes for preventing the flow of direct current through said path when a DC. voltage is applied across said path.

19. The system claimed in claim 18 further comprising A.C. power supply means connected in a circuit across said paths, said diodes having their anode electrodes connected to said conductors respectively and their cathode electrodes connected to ground, said diodes ineffective to prevent transmission of A.C. power through a path having a substantially zero DC. power supply voltage applied thereacross.

20. In a system for selectively transmitting information:

a. first and second conductor means;

b. source means providing a source of operating medium flow potential to said conductors;

c. a plurality of information transmitting paths connected in parallel across said conductors; said paths each'comprising at least an element rendered effective to enable medium flow through the path in response to the establishment of substantially zero source means flow potential across said path between said conductors;

d. one of said conductors having a finite extent, said paths connected to said one conductor at spaced locations along said extent and said one conductor constructed to provide impedance between said locations;

e. means for changing the potential along said one conductor whereby substantially zero potential is selectively established across said paths; second source means effective to enable transmission of information via a path in which said element is rendered effective; and,

g. output means operated in response to transmission of information via a path in which said element is rendered effective. 

1. In a system for trAnsmitting perceptible signals: a. first resistive conductor means; b. second conductor means; c. electric power supply means connected to said first and second conductor means; d. signal transmitting means defined by a plurality of separate parallel paths electrically connected between said first and second conductor means, said paths connected to said first conductor means at electrically spaced locations and each comprised of electrically responsive means rendered effective to transmit information in response to the application of substantially zero voltage differential across such path; and, e. selector means cooperatively related with said power supply means and at least one of said conductor means for selectively applying substantially zero voltage differentials across selected ones of said paths.
 2. A system as claimed in claim 1 further including signal means defining a source of information for tranmission by individual ones of said path when such paths are rendered conductive.
 3. A system as claimed in claim 2 further including a plurality of control means each associated with a respective parallel path, each of said control means governing the ability of its respective path to transmit a signal from said signal means when said path is rendered effective.
 4. The system claimed in claim 2 wherein said signal means comprises second electrical power supply means connected in a circuit across said paths, said circuit for said second power supply means being completable only through those paths which are rendered effective to transmit signals, and output means for detecting completion of a circuit across said second power supply means.
 5. The system claimed in claim 4 further comprising conditioning means associated with respective ones of said paths for controlling the conduction of a respective path which is rendered effective to transmit signals, said conditioning means having a first condition wherein a circuit through said respective path is interrupted when said path is rendered effective and a second condition wherein said respective path is conductive when rendered effective.
 6. The system claimed in claim 4 wherein said second power supply means comprises an alternating current source and said output means comprises at least an element for detecting alternating current power in a circuit connected across said second power supply means.
 7. A system as claimed in claim 1 wherein said power supply means comprises a D.C. power supply, and said selector means comprises an impedance element connected in circuit with said D.C. power supply means and said first conductor means, and mechanism for varying the impedance of said element.
 8. The system claimed in claim 1 wherein said first and second conductors comprise transparent sheets and said signal transmitting means comprises a body of liquid crystal material, said sheets disposed on opposite sides of said body of liquid crystal material to define a radiation transmitting assembly wherein signals in the form of radiation are passed through the assembly along paths extending through said conductors and said liquid crystal material, said power supply means providing a substantially steady state voltage across each of said sheets.
 9. The system claimed in claim 8 wherein the voltage across said sheets provides a transparent band extending across said sheets and through said liquid crystal material to enable electromagnetic radiation to pass through said sheets and crystal material along said band.
 10. The system claimed in claim 9 wherein said selector means is effective to shift the location of said band relative to said sheets and crystal material.
 11. The system claimed in claim 10 wherein said power supply means includes structure for providing a variable voltage output for adjustably controlling the width of the band.
 12. The system claimed in claim 8 further comprising a second radiation transmitting assembly juxtaposed with said first assembly, said seCond assembly comprising first and second transparent sheet-like conductors having a body of liquid crystal material interposed between them, power supply means for producing a substantially steady state voltage across each of said conductors of said second assembly, said first and second assemblies oriented with respect to each other so that the radiation transparent bands extend in directions transverse to each other to produce a radiation transparent aperture through said first and second assemblies.
 13. The system claimed in claim 12 further comprising second selector means associated with said second assembly, said first and second selector means operable to shift the positions of the respective radiation transmitting bands relative to said assemblies to adjustably change the location of said aperture relative to said assemblies.
 14. In a system for selectively transmitting information: a. means defining an electric power supply; b. first resistive conductor means connected across said power supply means; c. second conductor means connected across said power supply means; d. means defining a plurality of parallel information transmitting paths electrically connected between said first and second conductor means, said paths connected to said first conductor means at electrically spaced locations; e. each of said paths individually rendered effective to transmit information only when the power supply voltage applied across such path between said first and second conductors is substantially zero; and, f. selector means cooperatively related with said power supply means and at least one of said first and second conductor means for changing the power supply voltages applied across said paths so that said paths are selectively and individually rendered effective to transmit information.
 15. The system claimed in claim 14 further comprising means for transmitting information between said conductors via only said paths which are rendered effective.
 16. The system claimed in claim 15 wherein said means for transmitting information provides for the passage of electromagnetic energy through said paths which are rendered effective.
 17. The system claimed in claim 14 wherein said power supply means comprises a D.C. power supply and said paths each comprise at least a circuit element having a variable impedance to the passage of electromagnetic energy via said path, said circuit element having a first impedance when substantially zero power supply potential is applied across said path and a substantially different impedance when a power supply voltage differential is applied across said path.
 18. The system claimed in claim 17 wherein said at least one circuit element comprises first and second oppositely poled diodes for preventing the flow of direct current through said path when a D.C. voltage is applied across said path.
 19. The system claimed in claim 18 further comprising A.C. power supply means connected in a circuit across said paths, said diodes having their anode electrodes connected to said conductors respectively and their cathode electrodes connected to ground, said diodes ineffective to prevent transmission of A.C. power through a path having a substantially zero D.C. power supply voltage applied thereacross.
 20. In a system for selectively transmitting information: a. first and second conductor means; b. source means providing a source of operating medium flow potential to said conductors; c. a plurality of information transmitting paths connected in parallel across said conductors; said paths each comprising at least an element rendered effective to enable medium flow through the path in response to the establishment of substantially zero source means flow potential across said path between said conductors; d. one of said conductors having a finite extent, said paths connected to said one conductor at spaced locations along said extent and said one conductor constructed to provide impeDance between said locations; e. means for changing the potential along said one conductor whereby substantially zero potential is selectively established across said paths; f. second source means effective to enable transmission of information via a path in which said element is rendered effective; and, g. output means operated in response to transmission of information via a path in which said element is rendered effective. 